Think its cool, but what i don't like is that the empty "air space" of the bottle should be down, as if the coke is also lighter than air and floating also inside the bottle. It should be anxious to get out and fly up. But hasn't this idea been used already?

john--
this solution (along with many of the suggestions above) have all been done. Even recently.

A "diet" drink that has "floating" qualities is no longer an idea that separates it from other diet drinks. Plus, i think i would stay away from CocaCola (or Pepsi) when thinking of clients for your book.

That being said...here's another way to look at it: The drink is at the top of the glass with the FOAM at the bottom....implying the drink is lighter than the foam. mmmm, good idea, no?
even still, no cocacola in your portfolio

I think it's good to have ads fore big brands like Coca-Cola, Apple or Nike in your portfolio but it has to be really good. It's too easy to have only products that never advertise (like left-handes shops or beer with milk).

But you have too think further. What is the real insight? Why do people drink light products? How too keep the message fresh...?